Method and apparatus for reciprocal polishing

ABSTRACT

A polishing pad is located on a reciprocal motion generator. The polishing pad includes a plurality of discrete fluid channels. An abrasive article is located on the polishing pad. The abrasive article is reciprocally energized relative to the work piece. A fluid pressure in one or more of the discrete fluid channels is altered to selectively deform the abrasive article to preferentially remove material from the work piece.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of the filing date of U.S. Provisional Patent Application Ser. No. 61/232,525 filed Aug. 10, 2009, which is entitled “Method and Apparatus for Ultrasonic Polishing” which is hereby incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention is directed to a method and apparatus for reciprocal or alternating polishing, and in particular, user-controlled preferential material removal.

BACKGROUND OF THE INVENTION

Reciprocal excitation produces a relative motion responsible for material removal at the interface between an abrasive article and a work piece. The relative motion between the abrasive article and the work piece causes asperities to interlock and high stresses producing wear. During ultrasonic excitation a relative velocity is produced between the abrasives and the work piece that varies from zero to a maximum back to zero. The hydrodynamic film formed at the interface is negligible promoting maximum wear at the interface.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to an ultrasonic assembly with user controlled preferential material removal. The present ultrasonic polishing has wide application to polishing slider bars for hard disk drives, optical fibers, lenses, and the like.

A series of air/fluid channels located behind an abrasive article. The fluid pressure in the fluid channels can be changed to deform the abrasive article, causing localized high stresses between the abrasive article and a work piece. The localized high stress preferentially removes more material from the work piece at specific locations. Interference between the work piece and the abrasive article is controlled by the magnitude of the air/fluid pressure applied at the interface. An ultrasonic generator applies ultrasonic energy to the abrasive article with negligible out of plane motion.

The present invention is also directed to a method of polishing a work piece. A polishing pad is located on an excitation generator. The polishing pad includes a plurality of discrete fluid channels. The excitations generated oscillate or energize the abrasive article. An abrasive article is located on the polishing pad. Fluid pressure in one or more of the discrete fluid channels is selectively altered to selectively deform the abrasive article to preferentially remove material from the work piece.

In one embodiment a series of air/fluid ports are fabricated on the polishing pad to selectively deform the abrasive article, thus increasing or decreasing interference between the polishing article and the bar. This process may be very desirable for controlled sensor material removal as is the practice in disk drives, such as disclosed in U.S. Patent Application No. 2005/0071986 (Lackey et al.), which is hereby incorporated by reference.

In another embodiment, a series of pressure hoses are connected from the fixed base to the polishing pad to control the pressure in each air/fluid channel. The spatial distance between a series of sensors can be matched to the polishing plate channels to produce customized stress management at each work piece sensor. If the desired amount of wear is achieved at each sensor then the pressure is removed from the pressure channel causing no interference.

Reciprocal motion imparts interference between the work piece and the abrasive article and minimizes formation of a hydrodynamic film to maximize polishing and burnishing. Multiple lubricant viscosities can be used without the concern of interference mitigation due to hydrodynamic film formation. A boundary lubrication regime is preferably maintained throughout the polishing process.

Controlled interference between the abrasive article and the work piece can be maintained using a hydrostatic air bearing and/or preloaded gimbaled work piece holder. The work piece is presented to the abrasive article is such a fashion that the cutting forces emanating from the interaction are balanced and minimize chatter and vibrations. The work piece holder maintains stability during the polishing process.

Substrate actuation can impart preferred concave or convex shapes (crown, camber, etc.) to the work piece. Compact lapping tools capable of atomically smooth polishing bars. The floor space required for housing this tool is extremely small compared to spindle base lapping tools.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic sectional view of a reciprocal motion assembly in accordance with an embodiment of the present invention.

FIG. 2 is an exploded view of the reciprocal motion assembly of FIG. 1.

FIG. 3 is a schematic illustration of a reciprocal motion generator in accordance with an embodiment of the present invention.

FIG. 4 is a schematic sectional view of a reciprocal motion assembly with user-controlled preferential material removal in accordance with an embodiment of the present invention.

FIG. 5 is an enlarged view of a polishing pad in accordance with an embodiment of the present invention.

FIG. 6 is a schematic illustration of deformation of the abrasive article in accordance with an embodiment of the present invention.

FIG. 7 is a schematic illustration of a work piece being polished using preferential material removal in accordance with an embodiment of the present invention.

FIG. 8A is a schematic illustration of an alternate polishing pad and method in accordance with an embodiment of the present invention.

FIG. 8B is a schematic illustration of another alternate polishing pad and method in accordance with an embodiment of the present invention.

FIG. 9 is a perspective view of a polish pad with circular fluid channels in accordance with an embodiment of the present invention.

FIG. 10 is a gimballed work piece holder in accordance with an embodiment of the present invention.

FIG. 11 is hydrostatic clearance control mechanism in accordance with an embodiment of the present invention.

FIG. 12 is an exploded view of the clearance control mechanism of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 illustrate a reciprocal motion assembly 20 with a reciprocal motion generator 22 in accordance with an embodiment of the present invention. An excitation platform 28 is mounted to the ultrasonic generator 22. The excitation platform 28 includes a polishing pad 30 with an abrasive article 32 mounted thereon. The abrasive article 32 can be attached to the polishing pad 30 by a variety of techniques, including adhesives, vacuum, mechanical fasteners, high friction interface, and the like.

A variety of abrasive articles are suitable for use with the present a reciprocal motion assembly 20, such as for example, abrasive charged polymers, diamond charged flexible plates, diamond-like-carbon coated flexible plates, and the like. In one embodiment, the abrasive article includes a DLC film with a thickness of 50-200 nm with integrated cutting asperities with a height of 5-50 nanometers to provide high stress sites, and a thin film lubricant to provide boundary lubrication. Since deformation of the abrasive article 32 is typically in the nanometer range, the abrasive article 32 can be flexible, rigid, or semi-rigid.

FIG. 3 is a detailed illustration of the a reciprocal motion generator 22 in accordance with an embodiment of the present invention. Spring assembly 34 includes an X-springs 36 and a Y-spring 38 attached to anchor pads 26 by spring anchors 40. The anchor pads 26 retain the spring assembly 34 above the base 24 in a cantilevered configuration. In the illustrated embodiment, the X-Y springs 36, 38 for a generally rectangular shape with additional spring anchors 42 at the corners.

Electro-mechanical system 48 including a moving base 44 with a magnet that is actuated by alternating current applied to coil 46. Upon energizing of the coil 46, the springs 36, 38 are bent out of plane, which causes the attached moving base 44 to undergo a reciprocating motion. The motion of the moving base 44 can be elliptical, orbital, circular, and the like. Additional coils 46 can optionally be provided to generate irregular motions.

FIGS. 4 and 5 illustrate an alternate reciprocal motion assembly 50 with user-controlled preferential material removal in accordance with an embodiment of the present invention. Polishing pad 52 is mounted to ultrasonic generator 22 as discussed above. The polishing pad 52 includes a plurality of discrete fluid channels 54 fluidly coupled to one or more discrete ports 56. Each of the ports 56 is fluidly coupled to pressure control ports 58 on base 60 by one or more hoses 62. The fluid channels 54 can be linear, curvilinear, circular, concentric, or any other suitable configuration. The width and spacing between the fluid channels 54 can be regular or irregular. In one embodiment, abrasive article 64 is located directly on the fluid channels 54. In another embodiment, an intermediate membrane 66 extends across the fluid channels 54.

Controller 70 selectively adjusts fluid pressure in each of the discrete fluid channels 54. Upon activation the controller 70 adjusts the fluid pressure in the fluid channels 54 to deform the flexible abrasive article 64 and to increase or decrease interference with the work piece 72 being ultrasonically polished (see FIG. 7). The controller 70 can be hydraulic or pneumatic. In alternate embodiments, the deformation of the abrasive article 64 can be electromechanical, electrostatic, or a variety of other techniques.

FIG. 6 is a schematic side sectional view of the polishing pad 52 and abrasive article 64 during reciprocal polishing in accordance with an embodiment of the present invention. In the illustrated embodiment, positive pressure is delivered to each of the fluid channels 54 to deform the abrasive article 64 above the surface of the polishing pad 52. Protrusions 65 of the abrasive article 64 are exaggerated for illustration purposes. For most applications, the protrusions 65 will have a height 67 of less then one micrometer.

FIG. 7 illustrates the interference between a work piece 72 and the abrasive article 64 in accordance with an embodiment of the present invention. In the illustrated embodiment, work piece 72 is a slider bar containing a plurality of sliders 74A, 74B, 74C, 74D, 74E (collectively 74) for use in a hard disk drive. Each of the sliders 74 includes one or more read/write heads and/or sensors 76. In the illustrated embodiment, the amplitude of the ultrasonic motion imparted by the reciprocal motion generator 22 is preferably less than the size of the feature being polished, such as for example the sensors 76, in order to maintain the position of the protrusions 78 relative to the feature being polished.

Positive pressure is applied to fluid channels 54A, 54B, 54C and 54E, while no pressure is applied to fluid channel 54D. The present method and apparatus allows for selective polishing of the individual sliders 74. The read/write heads and/or sensors 76 can be adapted to provide a signal proportional to the progress of the polishing operation. In one embodiment, the sensors 76 are height sensors. Various control mechanisms are known for monitoring the progress of the polishing process, such as the closed loop feedback system disclosed in U.S. Patent Application No. 2005/0071986 (Lackey et al.), which is hereby incorporated by reference. Consequently, controller 70 can be programmed to automatically control the pressure in the fluid channels 54 in accordance with the polishing requirements for the work piece 72.

FIG. 8A illustrates an alternate polishing pad 100 in accordance with an embodiment of the present invention. The size and shape of the fluid channels 102 can be engineered for specific applications. The pressure in the fluid channels 102 can be positive, negative, or neutral. Consequently, the present method and apparatus can be used for polishing complex surfaces. For example, negative pressure is applied to fluid channel 102B, causing the abrasive article 104 to form a concave surface suitable for polishing curvilinear work piece 106, such as for example lenses, edges of fiber optics and the like. The abrasive article 104 can also be deformed to polish edges or fringes of a work piece to create a crown or camber.

FIG. 8B illustrates an alternate polishing pad 120 in accordance with an embodiment of the present invention. Instead of deforming abrasive article 122 on the level of each fluid channel 124, the abrasive article 122 is deformed on a macro level. In the illustrated embodiment, the abrasive article 122 assumes a curvilinear shape, such as may be used for polishing lens 126 or other optical elements.

FIG. 9 is a perspective view of an alternate polishing pad 140 with fluid channels 142 arranged concentrically in accordance with an embodiment of the present invention. Each of the discrete fluid channels 142 is fluidly coupled to one or more ports 144. The concentric arrangement of the fluid channels 142 is particularly useful for polishing circular objects, such as for example disks for a hard disk drive or lens, such as illustrated in FIG. 8B. In one embodiment, the work piece is rotated while engaged with the abrasive article, with or without ultrasonic vibration.

Interference control between the work piece and the abrasive article can be achieved using a variety of techniques, including hydrostatic or hydrodynamic fluid bearings, and/or a gimballed interface. Various methods and systems for interference control suitable for use with the present reciprocal motion assembly are disclosed in U.S. Provisional Patent Application Ser. No. 61/232,425, entitled Dressing Bar for Embedding Abrasive Particles into Substrates, filed Aug. 8, 2009; Ser. No. 61/174,472, entitled Abrasive Article with an Array of Gimballed Abrasive Members and Method of Use, filed Jun. 30, 2009, all of which are hereby incorporated by reference.

In one embodiment, the various work pieces discussed herein are supported by a gimbal mechanism. FIG. 10 is an exploded view of a work piece holder 150 that permits roll and pitch moments of work piece 152 during the polishing process. Work piece 152 is attached to gimbal mechanism 154. Spring assembly 156 includes dimple 158 that applies a point load to the gimbal mechanism 154.

FIGS. 11 and 12 illustrate a hydrostatic work piece holder 160 with an actuation mechanism 162 to bring the work piece 164 in contact with the abrasive article (see FIG. 4) in accordance with an embodiment of the present invention. A gimbal mechanism 166 holds the work piece 164. Pneumatic hoses 168 delivery externally pressured bed through ports 172 to create a hydrostatic air bearing between the abrasive article and the work piece holder 170. The gimbal mechanism 166 allows for movement of the work piece 164 with minimal bending and twisting during contact with the polishing media. The hydrostatic air bearing is preferably greater than the cutting forces, to stabilize the interface between the work piece 164 and the abrasive article.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the inventions. The upper and lower limits of these smaller ranges which may independently be included in the smaller ranges is also encompassed within the inventions, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either both of those included limits are also included in the inventions.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and described the methods and/or materials in connection with which the publications are cited.

The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

Other embodiments of the invention are possible. Although the description above contains much specificity, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.

Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. 

1. A polishing apparatus for polishing work pieces, the polishing apparatus comprising: a reciprocal motion generator; a polishing pad located on the reciprocal motion generator, the polishing pad having a plurality of discrete fluid channels; an abrasive article located on the polishing pad; and a controller fluidly coupled to the discrete fluid channels and programmed to selectively alter a fluid pressure in one or more of the discrete fluid channels to selectively deform the abrasive article to preferentially remove material from the work piece.
 2. The polishing apparatus of claim 1 wherein the fluid channels are configured in one of linear, curvilinear, or concentric pattern.
 3. The polishing apparatus of claim 1 further comprising sensors adapted to monitor material removal from the work piece.
 4. The polishing apparatus of claim 3 further comprising a closed-loop control system for polishing the work piece.
 5. The polishing apparatus of claim 1 further comprising a gimbal assembly connecting the work piece bar to a support structure, the gimbal assembly applying a preload that biases the work piece toward the abrasive article.
 6. The polishing assembly of claim 5 further comprising one or more actuators configured to alter the pitch and roll of the work piece relative to the abrasive article.
 7. The polishing apparatus of claim 1 further comprising a hydrostatic bearing assembly including a plurality of ports fluidly coupled to a source of compress air, the ports oriented toward the abrasive article to maintain a hydrostatic air bearing between the work piece and the abrasive article.
 8. The polishing apparatus of claim 1 wherein the abrasive article is one of flexible, rigid or semi-rigid.
 9. The polishing apparatus of claim 1 wherein the fluid channels are configured to create a crown or camber on the work piece.
 10. A method of polishing a work piece comprising the steps of: locating a polishing pad on a reciprocal motion generator, the polishing pad including a plurality of discrete fluid channels; locating an abrasive article on the polishing pad; reciprocally energizing the abrasive article relative to the work piece; and selectively altering a fluid pressure in one or more of the discrete fluid channels to selectively deform the abrasive article to preferentially remove material from the work piece.
 11. The method of claim 10 further comprising configuring the fluid channels in one of a linear, a curvilinear, or a concentric pattern.
 12. The method of claim 10 further comprising: monitoring sensors adapted to measure material removal from the work piece; and altering the fluid pressure in one or more of the discrete fluid channels in response to a signal from the sensors.
 13. The method of claim 12 further comprising controlling fluid pressure in the fluid channels in accordance with a closed-loop control system.
 14. The method of claim 10 further comprising: supporting the work piece with a gimbal assembly; and applying a preload to bias the work piece toward the abrasive article.
 15. The method of claim 10 further comprising actuating one or more actuators to alter the pitch and roll of the work piece relative to the abrasive article.
 16. The method of claim 10 further comprising creating a hydrostatic bearing between the work piece and the abrasive article.
 17. The method of claim 10 further comprising the steps of delivering a compressed gas to a plurality of ports on a work piece holder to maintain a hydrostatic air bearing between the work piece and the abrasive article.
 18. The method of claim 10 further comprising altering the pressure in one or more of the fluid channels to create a crown or camber on the work piece.
 19. The method of claim 10 wherein the work piece comprises one of machined metal parts, silicon wafers, slider bars for hard disk drives, lenses, or optical fibers. 